The present invention relates to torque converter by-pass elements of the type which are now employed in automatic transmission torque converters, and more particularly, to such elements of the type including a fluid coupling.
Torque converter type automatic transmissions have achieved widespread application and acceptance in motor- vehicles. Although generally satisfactory in this application, torque converter type automatic transmissions inherently involve a certain amount of slippage, and therefore, inherently result in losses in vehicle fuel economy. In an effort to minimize such slippage, and thereby increase fuel economy, efforts have been made to by-pass the torque converter with some type of relatively direct drive, which typically is activated when the vehicle is operating in the higher gear ratios, or above a predetermined vehicle speed. Although the term "by-pass" is used in regard to this type of element, those skilled in the art will understand theft the element is actually transmitting torque in parallel with the torque converter.
While such prior art direct drive by-pass elements have resulted in improvements in fuel economy, certain types of by-pass elements heretofore utilized have, under certain operating conditions, transmitted various driveline vibrations to the passenger compartment of the vehicle, causing degradation of the ride quality of the vehicle. In an effort to provide a by-pass element which would not transmit driveline vibration to the passenger compartment, those skilled in the art have utilized a viscous coupling as the by-pass element. Although the use of a viscous coupling as the by-pass element does serve to minimize the transmission of driveline vibration, it does still involve a certain amount of slippage and loss of fuel economy.
One type of device which is now well known to those skilled in the art, although not Vet in widespread commercial usage, is a device referred to as a "O-slip damper", an example of which is illustrated and described in U.S. Pat. No. 4,557,357, assigned to the assignee of the present invention and incorporated herein by reference. The O-slip damper of the above-incorporated patent is referred to as "O-slip" primarily because torque is transmitted through a pair of nested, helical springs, such that there is really no slip between the input and the output. However, there are oscillations and torsional vibration which must be damped, and for that purpose, the damper includes a viscous coupling capable of dampening oscillatory movement between the input and output.
Subsequently, similar devices have been developed wherein torque is transmitted initially (at relatively low speeds), and at relatively high levels of driveline vibration, through the torque converter, but with increasing vehicle speed (or decreasing drive line vibration), there is an increasing apply pressure tending to bias the entire damper assembly into frictional engagement with the torque converter housing, thus at least partially by-passing the torque converter. It has been determined that O-slip dampers engage over a very short time period, and therefore, the change from, for example, 500 rpm slip through the torque converter to 0 rpm slip through the O-slip damper also occurs over a very short time. The result may be a decrease in the quality of the ride, as perceived by the vehicle driver.
A different approach to the problem of achieving increased fuel efficiency without adversely affecting the ride quality may be seen in the lock-up clutch (by-pass element) illustrated in U.S. Pat. No. 5,125,486. The device of the above-incorporated patent includes drive and driven members which together define a viscous coupling. Therefore, at relatively low vehicle speeds, and at relatively high levels of driveline vibration, the torque converter is by-passed by the viscous coupling. The drive and driven members cooperate to define a cone clutch, which is engaged as vehicle speed increases, and apply pressure increases, moving the drive member axially until the cone clutch engages. After engagement of the cone clutch, the device operates in the manner of a O-slip device, with oscillations and torsional vibrations damped by a set of circumferentially arranged coil springs constituting a torsional damper. In the lock-up clutch of the referenced patent, the need for axial movement of one of the members of the viscous coupling, in order to achieve engagement of the cone clutch, results in a very difficult sealing arrangement for separating the viscous fluid from the ATF (Automatic Transmission Fluid). In addition, because the members of the viscous coupling comprise the confronting members of the cone clutch, after engagement of the cone clutch, and while operating on the coil springs, there is no longer any viscous damping of oscillation and torsional vibration.